First the log for the mail account that was supposed to create the tickets out of the mails:
osTicket is having trouble fetching emails from the following mail account: Benutzer: support@gerber-web.ch Server: imap.mail.hostpoint.ch Fehler: Can not authenticate to IMAP server: [AUTHENTICATIONFAILED] Authentication failed. 5 aufeinander folgende Fehler. Maximal sind 5 erlaubt Das können Verbindungsprobleme zum E-Mail-Server sein. Der nächste verzögerte Anmeldeversuch wird in ungefähr 10 Minuten erfolgen https://support.gerber-web.ch

and besides of that error, i also got immediately error logs für a Database query:

DB Error #1054

[SELECT COUNT(DISTINCT CASE WHEN A2.`state` = 'open' AND A2.`state` = 'open' AND A1.`dept_id` = 3 AND A3.`object_type` = 'T' THEN A1.`ticket_id` END) AS `q15`, COUNT(DISTINCT CASE WHEN A2.`state` = 'open' AND A2.`state` = 'open' AND A1.`dept_id` = 1 AND A3.`object_type` = 'T' THEN A1.`ticket_id` END) AS `q16`, COUNT(DISTINCT CASE WHEN A2.`state` = 'open' AND A1.`dept_id` = 1 AND A2.`state` = 'open' AND A1.`dept_id` = 1 AND B5.`value` LIKE '%bugreportongerber-web%' AND A3.`object_type` = 'T' THEN A1.`ticket_id` END) AS `q17`, COUNT(DISTINCT CASE WHEN (A1.`team_id` IN (1) OR A1.`staff_id` IN (1)) AND A2.`state` = 'open' AND (A1.`team_id` IN (1) OR A1.`staff_id` IN (1)) AND A2.`state` = 'open' AND (A1.`team_id` IN (1) OR A1.`staff_id` IN (1)) AND A1.`ticket_id` = Z1.`ticket_id` AND A3.`object_type` = 'T' THEN A1.`ticket_id` END) AS `q18`, COUNT(DISTINCT CASE WHEN A2.`state` = 'open' AND A3.`object_type` = 'T' THEN A1.`ticket_id` END) AS `q1`, COUNT(DISTINCT CASE WHEN (A1.`team_id` IN (1) OR A1.`staff_id` IN (1)) AND A2.`state` = 'open' AND (A1.`team_id` IN (1) OR A1.`staff_id` IN (1)) AND A2.`state` = 'open' AND A1.`staff_id` IN (1) AND A3.`object_type` = 'T' THEN A1.`ticket_id` END) AS `q6`, COUNT(DISTINCT CASE WHEN A2.`state` = 'closed' AND A2.`state` = 'closed' AND A1.`closed` BETWEEN '2020-05-18 00:00:00' AND '2020-05-18 23:59:59' AND A3.`object_type` = 'T' THEN A1.`ticket_id` END) AS `q9`, COUNT(DISTINCT CASE WHEN A2.`state` = 'open' AND A2.`state` = 'open' AND A1.`isanswered` = '1' AND A3.`object_type` = 'T' THEN A1.`ticket_id` END) AS `q3`, COUNT(DISTINCT CASE WHEN (A1.`team_id` IN (1) OR A1.`staff_id` IN (1)) AND A2.`state` = 'open' AND (A1.`team_id` IN (1) OR A1.`staff_id` IN (1)) AND A2.`state` = 'open' AND NOT A1.`staff_id` IN (1) AND A3.`object_type` = 'T' THEN A1.`ticket_id` END) AS `q7`, COUNT(DISTINCT CASE WHEN A2.`state` = 'closed' AND A2.`state` = 'closed' AND A1.`closed` BETWEEN '2020-05-17 00:00:00' AND '2020-05-17 23:59:59' AND A3.`object_type` = 'T' THEN A1.`ticket_id` END) AS `q10`, COUNT(DISTINCT CASE WHEN A2.`state` = 'open' AND A2.`state` = 'open' AND A1.`isoverdue` = '1' AND A3.`object_type` = 'T' THEN A1.`ticket_id` END) AS `q4`, COUNT(DISTINCT CASE WHEN (A1.`team_id` IN (1) OR A1.`staff_id` IN (1)) AND A2.`state` = 'open' AND A3.`object_type` = 'T' THEN A1.`ticket_id` END) AS `q5`, COUNT(DISTINCT CASE WHEN A2.`state` = 'closed' AND A2.`state` = 'closed' AND A1.`closed` BETWEEN '2020-05-18 00:00:00' AND '2020-05-24 23:59:59' AND A3.`object_type` = 'T' THEN A1.`ticket_id` END) AS `q11`, COUNT(DISTINCT CASE WHEN A2.`state` = 'closed' AND A3.`object_type` = 'T' THEN A1.`ticket_id` END) AS `q8`, COUNT(DISTINCT CASE WHEN A2.`state` = 'closed' AND A2.`state` = 'closed' AND A1.`closed` BETWEEN '2020-05-01 00:00:00' AND '2020-05-31 23:59:59' AND A3.`object_type` = 'T' THEN A1.`ticket_id` END) AS `q12`, COUNT(DISTINCT CASE WHEN A2.`state` = 'closed' AND A2.`state` = 'closed' AND A1.`closed` BETWEEN '2020-04-01 00:00:00' AND '2020-06-30 23:59:59' AND A3.`object_type` = 'T' THEN A1.`ticket_id` END) AS `q13`, COUNT(DISTINCT CASE WHEN A2.`state` = 'closed' AND A2.`state` = 'closed' AND A1.`closed` BETWEEN '2020-01-01 00:00:00' AND '2020-12-31 23:59:59' AND A3.`object_type` = 'T' THEN A1.`ticket_id` END) AS `q14` FROM `ost_ticket` A1 JOIN `ost_ticket_status` A2 ON (A1.`status_id` = A2.`id`) LEFT JOIN `ost_thread` A3 ON (A3.`object_type` = 'T' AND A1.`ticket_id` = A3.`object_id`) LEFT JOIN `ost_thread_referral` A4 ON (A3.`id` = A4.`thread_id`) LEFT JOIN `ost_staff` A5 ON (A4.`object_type` = 'S' AND A4.`object_id` = A5.`staff_id`) LEFT JOIN `ost_thread` A6 ON (A1.`ticket_id` = A6.`object_id` AND A6.`object_type` = 'C') LEFT JOIN `ost_thread_referral` A7 ON (A6.`id` = A7.`thread_id`) LEFT JOIN `ost_staff` A8 ON (A7.`object_type` = 'S' AND A7.`object_id` = A8.`staff_id`) LEFT JOIN `ost_team` B0 ON (A4.`object_type` = 'E' AND A4.`object_id` = B0.`team_id`) LEFT JOIN `ost_team` B1 ON (A7.`object_type` = 'E' AND A7.`object_id` = B1.`team_id`) LEFT JOIN `ost_department` B2 ON (A4.`object_type` = 'D' AND A4.`object_id` = B2.`id`) LEFT JOIN `ost_department` B3 ON (A7.`object_type` = 'D' AND A7.`object_id` = B3.`id`) JOIN `ost_form_entry` B4 ON (B4.`object_type` = 'T' AND A1.`ticket_id` = B4.`object_id`) LEFT JOIN `ost_form_entry_values` B5 ON (B4.`id` = B5.`entry_id`) WHERE ((A2.`state` = 'open' AND (A1.`staff_id` = 1 OR A5.`staff_id` = 1 OR A6.`object_type` = 'C' AND A8.`staff_id` = 1 OR A1.`team_id` IN (1) OR B0.`team_id` IN (1) OR A6.`object_type` = 'C' AND B1.`team_id` IN (1))) OR (A2.`state` IN ('open', 'closed') AND (A1.`dept_id` IN (1, 3, 4, 5) OR B2.`id` IN (1, 3, 4, 5))) OR A6.`object_type` = 'C' AND B3.`id` IN (1, 3, 4, 5))] Unknown column 'Z1.ticket_id' in 'field list'
 
 ---- Ablaufverfolgung ----
 #0 (root)/include/mysqli.php(200): osTicket->logDBError('DB Error #1054', '[SELECT COUNT(D...')
 #1 (root)/include/class.orm.php(3459): db_query('SELECT COUNT(DI...', true, true)
 #2 (root)/include/class.orm.php(3506): MySqlExecutor->execute()
 #3 (root)/include/class.orm.php(2093): MySqlExecutor->getArray()
 #4 (root)/include/class.orm.php(2043): HashArrayIterator->{closure}()
 #5 (root)/include/class.orm.php(2022): CallbackSimpleIterator->next()
 #6 (root)/include/class.orm.php(2031): CallbackSimpleIterator->rewind()
 #7 (root)/include/class.orm.php(1703): CallbackSimpleIterator->valid()
 #8 (root)/include/class.orm.php(1713): CachedResultSet->fillTo(9223372036854775807)
 #9 (root)/include/class.orm.php(1336): CachedResultSet->asArray()
 #10 (root)/include/class.orm.php(1359): QuerySet->all()
 #11 (root)/include/class.search.php(973): QuerySet->one()
 #12 (root)/include/class.search.php(905): SavedQueue::counts(Object(StaffSession), true)
 #13 (root)/include/staff/templates/queue-tickets.tmpl.php(111): SavedQueue->getCount(Object(StaffSession))
 #14 (root)/scp/tickets.php(539): require_once('/home/ch284888/...')
 #15 {main}
Log-Datum: Montag, 18. Mai 2020 um 21:09 IP-Adresse: 62.167.136.43

I can normally login to this support account over webmail. But I have to mention, my whole page was broken after some faulty settings for .htaccess over plugins, i managed to restore access and I have setup HTTP Headers ifs thats also important for this case? I don't see any console errors there.